The present invention relates to polymers such as biodegradable tri-block copolymers and biodegradable materials having desirable mechanical properties. The present invention further relates to membranes for preventing tissue adhesion, artificial dura mater, suture threads, implant preparations, and sustained-release drug bases, using such materials.
Polymers for a bio-material are required to have a variety of functionalities depending on their applications. Among such functionalities are non-toxicity such as non-pyrogenicity or non-allergenicity, mechanical properties to render the materials compatible with tissues and living bodies, ability to separate substances, and ability to release drugs in a sustained manner.
For example, anti-adhesion membrane for prevention of post surgical adhesion of tissue are required to have properties such as readiness to insert into tissue, non-adhesiveness and low irritancy to tissue, biodegradability for eliminating the need to extirpate the membrane, mechanical strengths and elasticity that result in high followability to follow movements of tissues.
However, the required functionalities are not necessarily provided in a well-balanced manner in conventional bio-materials, and hence, the need exists for novel materials in which these functionalities are well-balanced.
An ABA-type tri-block copolymer has been proposed in which the segment B is polyethylene glycol and the segment As, provided at opposite ends of the unit B, are hydrophobic poly-xcex2-benzyl-L-aspartate (which may be referred to simply as PBLA, hereinafter) or poly-xcex2-benzyl-L-glutamate (which may be referred to simply as PBLA, hereinafter) (Papers on polymers, vol. 42, No. 11, 731-738 (1985)).
In any of conventional ABA-type tri-block copolymers, however, the segment B, a polyethylene glycol segment, has a number average molecular weight of 6000 or less. Such tri-block copolymers cannot be used as a biodegradable material since they lack sufficient mechanical strength and degrade at an excessively high rate in vivo.
It is an objective of the present invention to provide copolymers such as tri-block copolymers that have biodegradability and good mechanical properties in a well-balanced manner and to provide biodegradable materials using such copolymers.
Another objective of the present invention is to provide membranes for preventing tissue adhesion, artificial dura mater, suture threads, implant preparations, and matrices for sustained drug release, which have biodegradability and good mechanical properties in a well-balanced manner and have various functionalities as a bio-material.
In an effort to address these objectives, the inventors have found out that polymers, such as tri-block copolymers, of particular molecular weights having a segment with modified hydrophobic amino acids on either end of a hydrophilic polyethylene glycol of a particular molecular weight exhibit a high strength, elasticity, low irritancy, and bioabsorbability, and completed the present invention.
According to the present invention, there is provided an A1BA2-type polymer having a number average molecular weight of 10000 to 600000, wherein the polymer is composed of a segment A1 and a segment A2 each including modified amino acids, and a segment B composed of polyethylene glycol with a number average molecular weight of 8000 or higher, the segment A1 being bonded to one end of the segment B while the segment A2 is bonded to the other end of the segment B.
According to the present invention, there is further provided a biodegradable material containing the A1BA2-type polymer.
According to the present invention, there is further provided a membrane for preventing tissue adhesion that is composed of the biodegradable material.
According to the present invention, there is further provided an artificial dura mater composed essentially of the biodegradable material.
According to the present invention, there is further provided a suture thread composed essentially of the biodegradable material.
According to the present invention, there is further provided an implant preparation composed essentially of the biodegradable material.
According to the present invention, there is further provided a sustained release drug base composed essentially of the biodegradable material.